One issue with existing molds for forming structures of molding substances (e.g., sand, snow, clay, wax) is that a vacuum may be created inside of the mold, making it difficult to separate the mold from the molded structure. Packing or otherwise compacting a molding substance in the mold is often desirable for creating a sturdier structure, but removing more air from the molding substance in this way increases the potential for creating a vacuum in the mold. In some cases, the created vacuum may be strong enough to resist removal of the mold from the structure (or vice versa), and in some cases the vacuum may even retain at least some of the molding substance in or on the mold during separation, or may otherwise cause the structure to break or lose structural integrity when separated from the mold.
This vacuum issue exists even with molds configured to be removed vertically, when gravity is available to act against the vacuum and assist in the separation process. For example, a created vacuum may still be strong enough to break a structure when a user attempts to remove a mold vertically (e.g., lifting an inverted concave mold off a sand castle). If the vacuum is strong enough, there is also the potential issue that when a user lifts a mold to remove it, she will lift the entire structure (i.e., still in the mold) from its intended place, creating a risk that the structure will separate above a surface, drop, and break on impact. Another issue with some types of vertically-removed molds (e.g., “fill-and-flip molds”) is that it is difficult to lift such molds without hitting and damaging the structure just created. A mold designed to be removed vertically is limited to forms that generally taper upward and do not have higher structural elements that are farther from a central axis than lower structural elements.